The world is a three-dimensional (3-D) place and the human brain is very effective at interpreting data when it is presented in a 3-D format. The human brain interprets a scene as being three-dimensional by a variety of visual clues from which it can extract information for depth perception. There have been many attempts to find an effective way of creating displays that take advantage of visual clues to provide a true 3-D window on the world with practical real-time motion.
The visual clues can be broken down to four main categories which may be replicated by a 3-D display technology. Although an individual eye only sees a two dimensional (2-D) image created on the retina, the observer""s brain works with the slightly different views from the two eyes to construct the third dimension of depth from which the brain can create a 3-D image. This process is called stereopsis. To achieve this result, a display must somehow channel a different view into each eye.
Another category is motion parallax, which relies on the relative apparent motion of objects in the field of view as the observer""s head moves vertically or laterally. To achieve this result, a display typically gauges and responds to the observer""s head motion.
The two other categories provide weaker visual clues. Using eye focusing and convergence feedback, the brain can obtain some information about the depth position of an object by sensing how strongly the eye lens is squeezed to bring the object into focus and the relative angles of the two eyes needed to make the object views converge within the brain. Because, eye focusing and convergence are weak visual clues, most 3-D display systems can operate with the observer focusing at a fixed distance, such as infinity or on a screen close to the observer.
In addition, software-based visual illusions can create weak visual clues within an image generator for display on a 2-D surface. These illusions include object perspective and shading, distance haze and movement parallax from camera motion. Software-based visual illusions are the easiest category of visual clues to produce. Indeed, most simulator and computer games produce these visual illusions by using 3-D worlds within the computer memory and processor before rendering on a 2-D surface.
One example of a three-dimensional display taking advantage of stereopsis includes a movable vertical slit in combination with an image source. The slit is moved between a plurality of positions in sequence with images displayed by the image source. The images can be viewed by a viewer with each image displaced in space based on the position of the slit.
An example of a 3-D display device which can provide both stereopsis and motion parallax is a head-mounted display (HMD) device. Miniature display screens within the HMD device are registered to and provide a respective image to each eye. A head tracking device can be combined with the HMD device to provide lookaround capability with observer head motion. Such systems are, however, limited to use by a single observer at any one time and transport delays can result in nausea and loss of equilibrium.
In most 3-D viewing situations, it is only necessary to provide parallax for motion in a plane occupied by both of the observer""s eyes (e.g. a horizontal plane). Although prior art systems can provide a stereoscopic image to an observer, they have a number of significant limitations. Such systems suffer from low image brightness, a narrow field of view, a small number of pupil slices, and a small image size. Although any one of these deficiencies could be improved using prior art techniques, such improvement would be at the expense of severe degradation of the other considerations.
In accordance with preferred embodiments of the invention, a three-dimensional display device includes a multiple pupil, multiple projection system which has its pupils abutted as close together as possible. Each projection system simultaneously images a respective image from an image source onto a common viewing optic. The viewing optic can include a Fresnel lens or a concave mirror in a folded system. The viewing optic images the exit pupil of the projection lenses onto a continuous array of viewing ports at a viewing space. Such a system provides a brighter, multiple view display with a wide viewing space projection.
In accordance with a first aspect of the invention, a display device includes a plurality of image sources and an image space having a plurality of discrete views. Each image source displays a plurality of sequential images of an object. Each view is optically coupled to a respective sequential image of the object.
A multi-projection optical system is preferably used to couple the views to the sequential images. The multi-projector optical system includes a plurality of projector lens assemblies, each registered to a respective image source. A plurality of addressable shutters are registered to each projector lens assembly. A common viewing assembly is registered to the projector lens assemblies to provide the multiple views. The common viewing assembly preferably includes a tunable optical diffuser to smear seams between the projector systems. The optical diffuser preferably includes an index matching medium.
Preferably, a controller is coupled to the image sources and the shutter elements. Each image source provides a respective view of a scene at a specific time. The shutters are arranged such that there are a plurality of slits optically aligned with each image source. The controller operates the image sources and the shutters to form a plurality of simultaneous images. An observer views two of these images at a time, one with each eye.
The above and other features of the invention, including various novel details of construction and combination of parts, will be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular embodiments of the invention are shown by illustration only and not as a limitation of the invention. The principal and features of this invention may be embodied in varied and numerous embodiments without departing from the scope of the invention.